WO2013048181A2 - Acier inoxydable duplex faiblement allié ayant de remarquables propriétés de résistance à la corrosion et de façonnage à chaud - Google Patents

Acier inoxydable duplex faiblement allié ayant de remarquables propriétés de résistance à la corrosion et de façonnage à chaud Download PDF

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WO2013048181A2
WO2013048181A2 PCT/KR2012/007919 KR2012007919W WO2013048181A2 WO 2013048181 A2 WO2013048181 A2 WO 2013048181A2 KR 2012007919 W KR2012007919 W KR 2012007919W WO 2013048181 A2 WO2013048181 A2 WO 2013048181A2
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stainless steel
duplex stainless
corrosion resistance
hot workability
content
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WO2013048181A3 (fr
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김지수
안상곤
김봉운
김광태
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주식회사 포스코
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Priority to US14/347,827 priority Critical patent/US10280491B2/en
Priority to EP12836056.7A priority patent/EP2762597B1/fr
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to a duplex stainless steel having a two-phase structure of austenite phase and ferrite phase, and more particularly, to lowering the content of expensive alloying elements such as Ni and Mo in the duplex stainless steel and improving corrosion resistance and hot workability. Alloy duplex or lean duplex stainless steel.
  • austenitic stainless steel which is known to have good workability and corrosion resistance, contains iron (Fe) as a base metal and contains Cr and Ni as main raw materials, and is suitable for various purposes by adding other elements such as Mo and Cu. It is developed in various steel grades. Austenitic stainless steel is a type of steel having excellent corrosion resistance and corrosion resistance, and contains 8% or more of Ni component by weight in low carbon. However, the Ni component has a problem in that price competitiveness is low due to a large fluctuation in cost due to an increase in price. Therefore, in order to compensate for this, much research has been made on the duplex stainless steel that can provide corrosion resistance equal to or higher than that of the austenitic stainless steel while lowering the Ni content.
  • the duplex stainless steel is a steel grade in which the austenitic and ferritic volume fractions occupy 35 to 65%, respectively.
  • the duplex stainless steel has a low Ni content and is economical and secures high strength as compared to conventional austenitic stainless steels. It is being spotlighted as steel for industrial facilities such as desalination, pulp, paper, and chemical facilities requiring easy and corrosion resistance.
  • interest in low-alloy duplex stainless steel has been increased, which eliminated expensive alloying elements such as Ni and Mo and added low-cost alloying elements in place of these elements to further increase the advantages of low alloying cost. It is becoming.
  • Such low alloy duplex stainless steels are commonly referred to as low alloy duplex stainless steels.
  • it is interpreted that a low alloy duplex and a lean duplex have the same meaning.
  • the duplex stainless steel has defects on the surface and edges of the sheet during hot deformation. Such defects tend to be caused by low alloy duplexes with reduced alloying elements. It gets worse with stainless steel.
  • the most weak temperature of the hot workability in the duplex stainless steel is known through a number of experiments, the low alloy duplex stainless steel species is weak in hot workability in the low temperature region of 800 ⁇ 900 °C range.
  • the surface temperature of the raw material is lowered to the temperature range by contact with the lower temperature roll, so that defects are easily generated at the surface and the edge of the raw material. . Therefore, it is necessary to improve the hot workability of the temperature range.
  • An object of the present invention is to lower the content of Cr, Mo, Ni components in low alloy or lean duplex stainless steel, but the base material corrosion resistance of austenitic stainless steel can be obtained at least equivalent corrosion resistance than stainless steel 304 or 304L steel To provide an alloy duplex stainless steel.
  • C greater than 0 and 0.06% or less
  • Si greater than 0 and 1.5% or less
  • Mn greater than 0 and 2% or less
  • Cr 19 to 23%
  • Ni 1.8 to 3.5%
  • Mo 0.5 to 1.0%
  • Cu 0.3 to 1.0%
  • N 0.16 to 0.30%
  • Al 0.16 to 0.30%
  • Al 0.16 to 0.30%
  • Al 0.16 to 0.30%
  • B 0.001 to 0.005%
  • Ca 0.001 to 0.01%, including the steel O of the stainless steel
  • the content is 0.01% or less, and the rest provides a low alloy duplex stainless steel excellent in corrosion resistance and hot workability including Fe and unavoidable impurities.
  • the Mn is preferably 1.5 to 1.8% by weight.
  • the stainless steel in the present invention while controlling the content of O by Al deoxidation, the Al is preferably added in the molten steel in a weight% of 0.018 ⁇ 0.045%.
  • the Ni is preferably 2 to 3% by weight.
  • the B is preferably 0.0025 to 0.0035% by weight.
  • the Ca is preferably 0.001 to 0.0085% by weight. More preferably, the Ca is 0.001% to 0.0035% by weight.
  • the B + Ca is preferably 0.0035 to 0.012% by weight.
  • the Creq value according to the following Formula (1) is 22.5 to 23.5, and the Nieq value according to the following (2) formula is preferably 9.5 to 11 in the composition of the stainless steel.
  • the hot workability index calculated by the following formula (3) is 75 or more.
  • the low-alloy duplex stainless steel is in the range of 40 to 60% by volume of the austenitic phase, 40 to 60% by volume of the ferrite phase.
  • the present invention is to produce a low alloy duplex stainless steel excellent in hot workability, there is an effect that can suppress the sheet material cracking defects and surface line defects in the production of sheet material.
  • CPT critical formula temperature
  • FIG. 2 is a view showing the effect of Al and O on the hot workability index in the low alloy duplex stainless steel according to an embodiment of the present invention.
  • FIG 3 is a view showing the effect of B and Ca on the hot workability index in the low alloy duplex stainless steel according to an embodiment of the present invention.
  • low alloy duplex stainless steels are disclosed in Japanese Patent Laid-Open No. 61-56267 and International Publication WO 2002/27056.
  • the low-alloy duplex stainless steel disclosed in Japanese Patent Laid-Open No. 61-56267 and International Publication WO 2002/27056 is standardized by ASTM A240, the former being S32304 (representative component 23Cr-4Ni-0.13N), the latter being S32101 (representative component 21Cr-1.5Ni-5Mn-0.22N).
  • the low-alloy duplex stainless steel has a microstructure in which the ferrite phase and the austenite phase coexist in metallurgical terms, but the stability of each phase is reduced as alloy elements such as Cr, Mo, and Ni, which stabilize each phase, are reduced.
  • the microstructure exists in the region where the austenite phase and the ferrite phase coexist on the Schaeffler diagram. Unlike the case, the austenite phase and the martensite phase coexist near each other. Therefore, it is easy to cause phase transformation in the microstructure during deformation, and it is necessary to add an appropriate alloying element to maintain the balance between the phases.
  • S32205 duplex stainless steel is known as one of representative steel grades of duplex stainless steel having a mixed structure of austenite phase and ferrite phase at room temperature.
  • the steel grade contains a large amount of Cr, Mo and N components to ensure high corrosion resistance, and contains 5% or more of Ni components by weight to secure a phase ratio.
  • the steel grade standardized by ASTM A240 includes Ni and Mo contents of 2.5% and 2.4% by weight in the case of S81921 steel, respectively.
  • These duplex stainless steels provide superior corrosion resistance than the corrosion resistance required in certain application areas, but there are some aspects that are not economically feasible because they contain large amounts of expensive Ni and Mo.
  • duplex stainless steel is a two-phase structure steel in which a ferrite phase and an austenite phase coexist.As the ferrite phase is mainly deformed due to the crystallographic difference between the ferrite phase and the austenite phase during hot deformation at high temperature, the ferrite / austenite phase interface is used. Cracks due to hot deformation are likely to occur.
  • the Mo element which is a ferrite stabilizing element
  • the solid-solution strengthening effect of the ferrite phase is weakened, and the austenite is stabilized by increasing the N content instead of Ni, which is an austenite stabilizing element.
  • U.S. Patent Application Publication No. US 2004/0050463 discloses, by mass%, C: 0.1% or less, Si: 0.05-2.2%, Mn: 2.1-7.8%, Cr: 20-29%, A stainless steel comprising Ni: 3.0 to 9.5%, N: 0.08 to 0.5%, Mo: 5.0% or less, W: 1.2 to 8.0%, the remainder consisting of Fe and other unavoidable impurities is disclosed.
  • the amount of Cu that inhibits the hot workability is limited, and the hot workability is improved by increasing the Mn content.
  • the increase in the Mn content may cause a decrease in the corrosion resistance due to the formation of MnS in the microstructure. Deterioration of characteristics is expected.
  • the mass% is C: 0.03% or less, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 20 to 30%, Ni: 1.0 to 11.0%, Cu: 0.05 to 3.0 %, Nd: 0.005 to 0.5%, sol. It contains one or two of Al: 0.001 to 0.1%, N: 0.1 to 0.5%, and Mo: 0.5 to 6.0% and W: 1.0 to 10.0%, and the rest consists of Fe and other unavoidable impurities.
  • Duplex stainless steel is disclosed.
  • the present invention reports that hot workability is improved by stabilizing P, which is segregated at the ferrite / austenite grain boundary, in particular, using Nd, a rare earth element.
  • P content of 0.05% or less can be obtained without using Nd, which is an expensive rare earth element, and P is known to cause brittleness at room temperature, although it segregates at grain boundaries. It is not expected to have a significant effect on the improvement of workability.
  • Mn is combined with S, the grain boundary segregation element in the steel, to form MnS inclusions, and the precipitated MnS in the microstructure acts as a starting point for pitting, thereby lowering the formal resistance of the base metal.
  • the inventors have noted the role of Mn in low alloy duplex stainless steel.
  • the content of S present in the steel must be managed at an extremely low content of 10 ppm or less, or the content of Mn is lowered.
  • the content of Mn increases austenite phase stability and nitrogen. It is difficult to completely exclude the Mn content in low-alloy duplex stainless steel with a low Ni content because of its high solubility.
  • the process load is severe during the steelmaking process step, it is necessary to design an alloy that can control the formation of MnS to ensure the official resistance of the base material while suppressing the formation of MnS.
  • the Cu content was added as 0.3% to 1.0% by mass.
  • Cu was added to the stainless alloy to stabilize and strengthen the passivation film, and was added to the alloying element having the effect of reducing the corrosion rate of the steel in the normal atmosphere.
  • it should be added in an appropriate content because it inhibits the hot workability of the base material.
  • the present inventors investigated and studied the correlation between alloying elements and hot workability in relation to the hot workability of the base material of the low alloy duplex stainless steel.
  • Al of the alloying elements added to the stainless steel is an element having a high affinity with O, and acts as a strong deoxidizer to lower the O steel content.
  • O present in the steel segregates in the grain boundaries of ferrite / austenite, ferrite / ferrite and austenite / austenite phases present in the microstructure, thereby lowering the cleanliness of the grain boundary, and the grain strength is lowered by lowering the grain boundary cleanness. It is lowered, making it more susceptible to cracking.
  • S is known as a representative impurity that segregates at grain boundaries and inhibits the hot workability of materials, and many researches and processes have been developed and applied to reduce the content of S.
  • the formation of stable CaS by the addition of Ca is suppressed to prevent segregation of S at the grain boundary, while a small amount of Al is added to increase the content of O present in the steel by mass%. By limiting it to 0.01% or less, the effect of O on the hot workability of the material was minimized.
  • B was essentially added to improve the hot workability of the base material.
  • B improves the hot workability of the material by strengthening the grain boundary, but if contained in a large amount, it is important to add it in an appropriate amount because it adversely affects continuous casting.
  • the inventors have found a hot work index in consideration of alloying elements as a method of determining whether or not the hot workability of low alloy duplex stainless steel is good.
  • the reduction of area (RA, Reduction of Area) is the lowest value at 900 °C in the hot workability evaluation of low-alloy duplex stainless steel, in the present invention hot rolling when the RA value of 900 °C is 75 or more It has been found that the decay phenomenon is significantly reduced.
  • the hot work index is Al, Ca, and B, which are essential for improving hot workability, in addition to C, Si, Mn, Cr, Ni, Mo, Cu, and N, which are representative alloy elements included in low alloy duplex stainless steel.
  • the elements for stabilizing ferrite phases such as Cr, Mo, and Si are represented by Creq values
  • the elements for stabilizing austenite phases such as C, Mn, Ni, Cu, and N are represented by Nieq values.
  • C greater than 0 and 0.06% or less
  • Si greater than 0 and 1.5% or less
  • Mn greater than 0 and 2% or less
  • Cr 19 to 23%
  • Ni 1.8 to 3.5%
  • Mo 0.5 to 1.0%
  • N 0.16 to 0.30%
  • Cu 0.16 to 1.0%
  • the rest contains Fe and unavoidable impurities.
  • the alloy cost is lower than that of the austenitic stainless steel, and the formal resistance of the base material can be secured, and the corrosion resistance of the front surface can be secured to expand the use of the steel.
  • industrial contributions are extremely large.
  • the content of small steel O is limited to 0.01% or less.
  • the Creq, Nieq value and the section reduction rate RA were controlled.
  • the value is in the range of 22.5 to 23.5, and in the case of Equation (2), it is controlled in the range of 9.5 to 11.
  • the section reduction rate RA it controls so that the value obtained by Formula (3) may be 75 or more.
  • the Cr and Ni equivalents can be indexed by the content of each alloying element added to the material, and the hot workability of the material by comprehensively considering the effect of these alloying elements on the hot workability index.
  • a low alloy duplex stainless steel having excellent hot workability having a hot workability index of 900 ° C. having a value of 75 or more can be obtained.
  • the volume fraction of the austenitic phase is 40 to 60%, and the volume fraction of the ferrite phase is 40 to 60%.
  • C is an element effective for increasing the material strength by strengthening solid solution, but when the content is excessive, carbide forming element such as Cr, which is effective for corrosion resistance at ferrite-austenite phase boundary, is easily combined to lower the Cr content around the grain boundary to reduce corrosion resistance.
  • carbide forming element such as Cr, which is effective for corrosion resistance at ferrite-austenite phase boundary, is easily combined to lower the Cr content around the grain boundary to reduce corrosion resistance.
  • the C content is preferably made 0.06% or less.
  • Si is partially added for the deoxidation effect, but also partially added because it also acts as a ferrite stabilizing element. If excessive, the mechanical properties related to impact toughness are reduced, so it is limited to 1.5% or less.
  • Mn is generally contained in an amount of about 1.5% to control the melt flow rate, but the content may be increased for expensive Ni replacement, and in this case, it may additionally improve the hot workability.
  • the Mn content is limited to 2% or less.
  • the most preferred content of Mn in the present invention is 0.15 to 0.18%, which is less than 2%.
  • P is preferably managed as low as possible because segregation in grain boundaries or upper boundary systems can inhibit corrosion resistance and toughness. Therefore, it is desirable to limit it to 0.03% or less for the efficiency of the refining process.
  • S is segregated at the austenite-ferritic interface to deteriorate hot workability or to deteriorate corrosion resistance by the formation of MnS. Therefore, it is desirable to control the content as low as possible, so it is preferable to manage it at 0.002% or less.
  • Cr is a ferrite stabilizing element together with Mo, and plays a major role in securing the ferrite phase of Durex stainless steel, and is also an essential element for securing corrosion resistance. Increasing the content increases the corrosion resistance, but the expensive Ni content should also be increased proportionally to maintain the phase ratio. Therefore, the Cr content is increased by 19 to 23% to ensure the proper corrosion level while maintaining the phase ratio of the low alloy duplex stainless steel. Limited to
  • Ni is an austenite stabilizing element and plays a major role in securing the phase fraction of the austenitic phase of duplex stainless steel. Expensive reduction of Ni content for cost reduction can be offset by increasing content of Mn and N, which are other austenite phase forming elements, but excessive decrease of Ni content is due to excessive Mn and N content, but rather reduced corrosion resistance and hot workability or Cr And it is difficult to ensure the corrosion resistance due to the decrease in the content of Mo, Ni content is limited to 1.8 ⁇ 3.5%. Ni is preferably 2 to 3% by weight.
  • Mo is a ferrite stabilizing element like Cr and a strong corrosion resistance improving element.
  • Mo is a very expensive element, and if the content is excessive, there is a disadvantage in that the sigma phase is easily formed during heat treatment to lower the corrosion resistance and impact toughness.
  • the role of Mo is to secure a secondary role of Cr and to ensure proper corrosion resistance to secure an upper fraction, and in order to reduce manufacturing costs, the content of Mo is limited to 0.5 to 1.0%.
  • Cu is known as an element to stabilize the austenite phase, such as Ni, Mn and N, and is known to increase the corrosion resistance of stainless steel in sulfuric acid atmosphere.
  • the Cu content of more than 1% is known to reduce the formal resistance, and is known as an element that reduces the hot workability of stainless steel, it is preferable to limit the content of Cu to 0.3 ⁇ 1.0%.
  • N In duplex stainless steel, N is one of the elements that contributes to stabilization of the austenite phase together with Ni, and the increase in N content may additionally increase corrosion resistance and high strength. However, if the content of N is too high, it decreases the hot workability and lowers the error rate. On the other hand, if the content of N is too low, Cr and Mo content must be lowered to secure the phase fraction, and it is difficult to secure the weld strength and phase stability. Therefore, the N content is preferably limited to 0.16 to 0.30%.
  • the low alloy duplex stainless steel of the present invention is to contain Al, B, Ca further.
  • Al is an important element for deoxidation of stainless steel, and an addition of 0.003% or more is required to reduce oxygen in the steel.
  • Al is an element having a relatively high affinity with N, and when added excessively to form AlN to inhibit the toughness and corrosion resistance of the base material, limiting the content of Al to 0.003 ⁇ 0.05%.
  • the calcined oxygen O is a harmful element constituting the oxide which is representative of the nonmetallic inclusions, and when excessively contained, it becomes segregated at the grain boundaries and reduces the cleanliness of the grain boundaries, thereby inhibiting the hot workability of the material.
  • the excessively contained O may cause surface scratches when coarse cluster-shaped oxides are formed, so the content of steel O is at most 0.01%.
  • the preferred amount of Al to be added to the molten steel for this purpose is 0.018 ⁇ 0.045% by weight.
  • B is known as an element that segregates at grain boundaries to strengthen grain boundaries, and it is preferable to contain 0.001 to 0.005% in order to improve hot workability.
  • the B is 0.0025 to 0.0035% by weight.
  • Ca is an element that combines with S, a grain boundary segregation element, to form a stable CaS compound to suppress grain boundary segregation of S, thereby improving the hot workability of the material. However, if it is contained in an excessive amount may inhibit the weldability, it is preferable to limit the content to 0.001 ⁇ 0.01%. Preferably the Ca is 0.001 to 0.0035% by weight.
  • the content of B + Ca is preferably added at least 0.0035% to 0.012% at the same time to improve the hot workability.
  • 3 shows the change in hot workability index according to the content of such B + Ca.
  • the B + Ca content exhibits a hot workability index of 0.0035% or more. It can be seen that the cross-sectional area reduction ratio RA (Reduction of Area,%) is greater than 75.
  • Cr equivalent Cr equivalent of the following formula ⁇ 1> is generally known as an index in which the influence of Cr, Mo, Si, and Nb, which are ferrite generating elements, is converted into the influence of Cr in stainless steel.
  • Nb since Nb is not included in the alloy components, the Nb term was excluded from the Cr equivalent formula.
  • the degree to which the alloying elements of Cr, Mo, and Si contribute to the stability of the ferrite phase can be indexed, and the balance between the ferrite phase and the austenitic phase in the low alloy duplex stainless steel with reduced Ni content
  • the value of Cr equivalent should be 22.5 or more and 23.5 or less and limited the range of Cr equivalent.
  • Ni equivalent (Nieq) value in this invention is demonstrated.
  • the Ni equivalent in the following formula ⁇ 2> is an index in which the influence of Ni, Cu, N, which are austenite generating elements, in the stainless steel is converted.
  • the Ni content was limited to 1.8 to 3.5%, and based on this, the content of each alloying element was adjusted to balance the ferrite phase and the austenite phase.
  • the Ni equivalent value in the low alloy duplex stainless steel of the present invention should be 9.5 or more and 11 or less, and limited the range of Ni equivalent values.
  • the cross-sectional area reduction rate in Table 2 to be described later is shown to be lower than 75%.
  • the hot workability of the duplex stainless steel is evaluated by the rate at which the cross-sectional area of the material decreases when the material is heated at a specific temperature and uniaxially tensioned.
  • the ratio of cross-sectional area reduction can be expressed by the hot workability index called RA (Reduction of Area,%), and the RA value tends to increase proportionally with increasing temperature.
  • RA Reduction of Area,%
  • the present inventors have repeated experiments that improving the RA value at 900 ° C is a representative value for improving the hot workability of the entire material.
  • the minimum value of the 900 °C RA value was used as a range of hot workability index.
  • the hot workability of the duplex stainless steel is greatly affected by the type and content of alloying elements included in the material.
  • the content of elements such as O and S which tend to be segregated at grain boundaries, is greatly influenced, it is necessary to reduce the content of such grain boundary segregation elements.
  • deoxidation should be efficiently performed in the steelmaking process of duplex stainless steel, and Si deoxidation was mainly performed by the existing deoxidation method, but there was a limit in reducing the content of O to 50 ppm or less.
  • the hot work index could be expressed as a relation with the alloying element content included in the low alloy duplex stainless steel, and the minimum value of the hot work index should be 75 or more, thereby limiting the range.
  • % With respect to the component of Formula ⁇ 3> of this invention means the mass%.
  • the volume fraction of the austenite phase and the ferrite phase of the present invention will be described.
  • the volume fraction of the austenite phase is limited to 40 to 60%
  • the volume fraction of the ferrite phase is limited to the range of 40 to 60%.
  • This causes a problem of poor toughness when the volume fraction of the austenite phase is less than 40%, and a decrease in hot workability when more than 60%. In any case, corrosion resistance is lowered. Therefore, when the solution heat treatment is performed at around 1050 ° C., which is a typical condition in duplex stainless steel, in order to ensure the fraction of the austenite phase and the ferrite phase, Ni, which is an austenite phase increase element, is within the scope of the present invention.
  • specimens of low-alloy duplex stainless steels for the component composition range according to the present invention were prepared and measured in terms of phase fraction, corrosion resistance, and hot work index.
  • Table 1 the invention example and the comparative example are shown together, and remainder other than the component described in Table 1 is Fe and an unavoidable impurity element.
  • steel No.1 in Table 1 is a component system of STS304 steel, and the corrosion resistance of the steel of the present invention was adjusted to have corrosion resistance equal to or higher than that of steel No.1.
  • Table 2 was evaluated for the electrochemical corrosion resistance for the comparative example and the invention example, and the results of the evaluation of the percentage of the ferrite phase and hot workability index in the microstructure, respectively.
  • Creq, Nieq, and RA of Table 2 mean following formula ⁇ 1>, ⁇ 2>, and ⁇ 3>, respectively.
  • a low alloy duplex stainless steel having such a component was melted by a 50 kg vacuum induction furnace in a laboratory and cast into a steel ingot having a thickness of 150 mm, a width of 150 mm, and a length of 250 mm.
  • the raw material for hot rolling was processed from the ingot, heated at a temperature of 1250 ° C. for 1 to 2 hours, and then rolled under conditions of a finishing temperature of 950 ° C. to 850 ° C. to obtain a hot rolled post-steel sheet having a thickness of 12 mm x about 3000 mm.
  • spray cooling was performed to the temperature of 200 degrees C or less in the state whose steel material temperature immediately after rolling is 800 degreeC or more.
  • Final solution heat treatment was performed under water cooling conditions after cracking at 1050 ° C. for 30 minutes. However, the final solution heat treatment of No. 1 steel grade was performed under the conditions of water cooling after cracking at 1100 degreeC for 30 minutes.
  • the corrosion resistance evaluation test was done using the thick steel plate of 12 mm of plate thickness manufactured above as a base material.
  • Corrosion resistance evaluation experiments were evaluated using an electrochemical method called the coin-top anodic polarization test.
  • the conditions of the polarization test were to polish the surface of the specimen with sandpaper Nos. 60, 120, 320, and 600, and then expose only the surface area of 1 cm2 and cover the other surface with masking tape so that the test solution did not touch the other surface of the specimen. It was not.
  • an electric potential was applied by immersion in a 3.5% NaCl solution maintained at 30 ° C., and the electric potential at which the formula was generated was measured.
  • the cross section parallel to the rolling direction of a thick steel plate was buried in resin, mirror-polished, electrolytic etching was performed in KOH aqueous solution, and ferrite phase fraction was measured by performing image analysis by optical microscope observation.
  • the specimen was machined in a thick steel sheet having a thickness of 12 mm so that the direction parallel to the rolling direction was the longitudinal direction of the specimen, and the size of the specimen was processed in the form of a round rod having a length of 110 mm x 10 mm in diameter.
  • the specimen processed by the above method was heated to 1250 ° C. at an average temperature increase rate of 20 ° C./s, and maintained for 3 minutes after reaching the target temperature. Uniaxial tension was carried out at a stroke speed of 30 mm / s.
  • the test temperature was set at 100 ° C. interval from 800 ° C. to 1200 ° C., and the RA value was obtained by dividing the cross-sectional area of the specimen after the initial cross-sectional area.
  • the value used as RA value in this invention was made into RA value in 900 degreeC.
  • Figure 1 is a view showing the critical formula temperature (CPT) in the low alloy duplex stainless steel according to an embodiment of the present invention.
  • Figure 3 is a low alloy duplex stainless steel according to an embodiment of the present invention It is a figure which shows the influence of B and Ca on a hot work index.
  • the RA value was low.
  • the edge crack became more than 20 mm (No. 2, 8, D, E).
  • RA value was significantly increased by the addition of B, Ca, and Al, and the RA value was more than 75% at 900 ° C., which showed a good shape without edge cracking (No. A, B, C, D, F).
  • the oxygen content was 50 ppm or less, but the edge shape of the plate showed a good shape even when the oxygen content was 100 ppm or less (No. 6, 7, C).
  • the hot workability of the material is affected by major alloying elements such as Cr, Ni, Mn, Mo, and N, but also by trace additive elements such as Al, B, and Ca.
  • major alloying elements such as Cr, Ni, Mn, Mo, and N
  • trace additive elements such as Al, B, and Ca.
  • FIG. 3 it can be seen that trace additive elements such as B and Ca stabilize S in the steel, thereby improving the hot workability of the material.
  • Ca shows an example of the present invention introduced in the range of 0.001 ⁇ 0.01%.
  • the present invention it is possible to provide a low-alloy duplex stainless steel having low alloy cost and excellent corrosion resistance as compared to conventional austenitic stainless steel, and edge cracking due to hot workability inferiority, which is a major problem of low-alloy duplex stainless steel. Can be suppressed. As a result, the production load of the low alloy duplex stainless steel can be reduced, and it can be used in place of the expensive austenitic stainless steel to improve the economic efficiency, which is industrially useful.

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Abstract

La présente invention se rapporte à un acier inoxydable duplex faiblement allié qui est utilisé, par exemple, dans un équipement industriel comprenant un équipement de dessalement, un équipement industriel de fabrication de papier et de pâte, un équipement chimique et un équipement de construction. Cet acier inoxydable duplex faiblement allié présente de remarquables propriétés de résistance à la corrosion et de façonnage à chaud et contient, sur une base de pourcentage en poids, plus de 0 et pas plus de 0,06 % de C, plus de 0 et pas plus de 1,5 % de Si, plus de 0 et pas plus de 2 % de Mn, de 19 à 23 % de Cr, de 1,8 à 3,5 % de Ni, de 0,5 à 1,0 % de Mo, de 0,3 à 1,0 % de Cu et de 0,16 à 0,30 % de N, et comprend en outre de 0,003 à 0,05 % d'Al, de 0,001 à 0,005 % de B et de 0,001 à 0,01 % de Ca, et la teneur en acier brut dans l'acier inoxydable ne dépasse pas 0,01 %, et le reste est constitué de fer et d'impuretés inévitables.
PCT/KR2012/007919 2011-09-28 2012-09-28 Acier inoxydable duplex faiblement allié ayant de remarquables propriétés de résistance à la corrosion et de façonnage à chaud WO2013048181A2 (fr)

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US14/347,827 US10280491B2 (en) 2011-09-28 2012-09-28 Low-alloy duplex stainless steel having outstanding corrosion resistance and hot working properties
EP12836056.7A EP2762597B1 (fr) 2011-09-28 2012-09-28 Acier inoxydable duplex faiblement allié ayant de remarquables propriétés de résistance à la corrosion et de façonnage à chaud

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KR1020110098320A KR20130034349A (ko) 2011-09-28 2011-09-28 내식성 및 열간가공성이 우수한 저합금 듀플렉스 스테인리스강
KR10-2011-0098320 2011-09-28

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KR20160080304A (ko) * 2014-12-26 2016-07-08 주식회사 포스코 심가공 특성이 우수한 듀플렉스 스테인리스강
EP3418416B1 (fr) * 2016-02-17 2020-12-02 Nippon Steel & Sumikin Stainless Steel Corporation Matériau en acier inoxydable biphasique ferritique-austénitique et son procédé de fabrication
CN108396223B (zh) * 2018-03-29 2020-09-29 东北大学 一种超级奥氏体不锈钢及其合金成分优化设计方法
CN112063919B (zh) * 2020-07-31 2021-11-26 丽水市正阳电力设计院有限公司 一种双相不锈钢

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EP2762597A4 (fr) 2015-08-19
US10280491B2 (en) 2019-05-07
KR20130034349A (ko) 2013-04-05
US20150267285A1 (en) 2015-09-24
EP2762597B1 (fr) 2017-02-01
WO2013048181A3 (fr) 2013-05-23

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